Why are individuals without a spleen at increased risk for severe infection?

Why are individuals without a spleen at increased risk for severe infection?

• A. Spleen clears encapsulated organisms; risk of sepsis from Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae
• B. Due to increased RBC sequestration
• C. Because the liver takes over immune function
• D. They have enhanced immune response to encapsulated organisms

Answer: (A)

The key idea is that the spleen is a major defense against encapsulated bacteria by filtering bacteria from the bloodstream and mounting an antibody-mediated response that promotes opsonization and phagocytosis. Without a spleen, the body's ability to clear encapsulated organisms such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae diminishes, making individuals much more susceptible to severe, rapidly progressing infections and sepsis from these pathogens. The spleen contains marginal zone B cells that produce IgM and supports opsonization and complement activation, which helps macrophages engulf encapsulated bacteria. When the spleen is absent, this protective mechanism is weakened, so bacteremia can occur more easily and become life-threatening. Other options don’t fit as well because increased red blood cell sequestration is not the primary reason for infection risk, the liver cannot fully compensate for splenic immune functions, and the immune response to encapsulated organisms is not enhanced—in fact, there is a deficiency that raises infection risk.

The key idea is that the spleen is a major defense against encapsulated bacteria by filtering bacteria from the bloodstream and mounting an antibody-mediated response that promotes opsonization and phagocytosis. Without a spleen, the body's ability to clear encapsulated organisms such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae diminishes, making individuals much more susceptible to severe, rapidly progressing infections and sepsis from these pathogens.

The spleen contains marginal zone B cells that produce IgM and supports opsonization and complement activation, which helps macrophages engulf encapsulated bacteria. When the spleen is absent, this protective mechanism is weakened, so bacteremia can occur more easily and become life-threatening.

Other options don’t fit as well because increased red blood cell sequestration is not the primary reason for infection risk, the liver cannot fully compensate for splenic immune functions, and the immune response to encapsulated organisms is not enhanced—in fact, there is a deficiency that raises infection risk.